Photodiodes have in the past been utilized for a number of applications wherein light levels are sensed and a current output produced directly related to the ambient light. One example of a prior art system is an ambient light sensor for sensing the approach of an oncoming motor vehicle and automatically dimming a high beam headlamp to eliminate the need for motor vehicle operator actuation of a dimmer switch. Another representative use of a photodiode is for sensing light levels in an optical character recognition system where reflected light from a document is scanned by a character reader which converts the reflected signal from the paper to a digital signal corresponding to the characters on the document.